First off we’re working with a 1950, absolutely stock 216 with the original Rochester and single stage AC glass bowl fuel pump with an AC sediment bowl filter in between the two. About everything involved here has been completely and meticulously dismantled and brought back to factory specs within the past couple of thousand miles. That is, the carburetion, ignition and mechanical such as the head completely redone.
Well earlier this summer I posted a thread about a sudden backfire through the carb that occurred during a normal drive. It happened only once then all was fine on the ride home. Since then I have had it happen on a couple of more outings over the summer, just one loud bang which causes the hood and cowl vent to take a little jump then all is fine. At first I passed it off as possibly a tiny piece of carbon causing a hot spot in the cylinder since I couldn’t find anything out of spec.
All of my driving is just to keep the old gal limbered up, just pleasure drives. Most of my drives are not more than twenty or thirty miles one way and usually only once or twice a week. A few weeks ago I was coming home from a drive and all of a sudden the engine lost power, like it was running out of fuel and started backfiring through the carburetor when I fed it throttle. The first thought was plugged fuel line/filter or pump going bad. But, if I kept the pedal all the way down to the floor then I could at least keep it running without backfiring and although it was very sluggish and lacked power I could nurse it up to 50 or 55mph. If I backed off on the throttle then I could feel the power completely drop off and if I slowly tried applying power it would go on it’s nose and backfire more. So since it would run up to highway speed I think I eliminated fuel starvation. Still when I got it home I pulled the Rochester apart and checked everything inside and all was clean, clear and in adjustment. I reinstalled the carb and drove it for a couple of more weeks without incident.
Yesterday I took a ten-mile drive to see a buddy and she ran real nice and smooth out to his house. We BS’ed for a 35 or 40 minutes and I started home. A block away from his house she started to backfire whenever I added partial power and would just die out, given full throttle I could again at least keep the R’s up enough to get it home at highway speed.
Once home in the garage I checked the fuel flow through the glass and fuel was flowing free and clear. I pulled the plugs and they looked fine and all were firing every time with the plug tester. Pulled the cap and rotor, they looked fine, points looked fine and gap was proper and plug wires are new a few thousand miles ago. Pulled the valve cover and checked the clearances, all that was fine. I started her up and checked the valve movement, all were fine and all the push rods were taking a nice little quarter turn every click. Checked the timing and she’s riding right on the ball at idle and advances as you bring up the R’s. Checked the vacuum at the manifold and that was correct and steady.
Sitting parked in the garage when I revved it up it takes the fuel fine, no backfiring no hesitation.
So this one has me absolutely baffled. You hope that when you nurse it home and start to look that you will find a broken rotor, or trace in the cap or vacuum leak or that the timing slipped or bad advance or plugged fuel circuit, or stuck valve, but notta thing seems to be out of place.
I’ve got a beautifully prepared Carter W-1 sitting on the bench that I was going to try this week but I don’t want to take a chance on adding another problem until I figure out what is causing this erratic loss of power and backfire.
Once again, I’m open to all opinions, don’t mean I’ll take all of your advice but I sure will give it some consideration.
Denny Graham
Sandwich, IL
Last edited by Denny Graham; 08/19/2008 5:09 PM.
